XML 96 R71.htm IDEA: XBRL DOCUMENT v3.24.0.1
Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) - Square Butte - Square Butte PPA
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
MW
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Power Purchase Agreements [Line Items]      
Ppa counterparty total debt outstanding $ 171.8    
Minnesota Power      
Power Purchase Agreements [Line Items]      
Cost of purchased power 86.2 $ 82.7 $ 82.4
Pro rata share of ppa counterparty interest expense $ 5.5 $ 5.1 $ 5.8
Square Butte Coal-fired Unit      
Power Purchase Agreements [Line Items]      
Generating capacity counterparty owned (MW) | MW 455    
Square Butte Coal-fired Unit | Minnesota Power      
Power Purchase Agreements [Line Items]      
Expected output entitlement 50.00%    
Ppa annual debt service obligation 50.00%    
2024-01-01 | Square Butte Coal-fired Unit | Minnesota Power      
Power Purchase Agreements [Line Items]      
Ppa counterparty annual debt service through 2027 $ 33.5    
2025-01-01 | Square Butte Coal-fired Unit | Minnesota Power      
Power Purchase Agreements [Line Items]      
Ppa counterparty annual debt service through 2027 29.5    
2026-01-01 | Square Butte Coal-fired Unit | Minnesota Power      
Power Purchase Agreements [Line Items]      
Ppa counterparty annual debt service through 2027 29.6    
2027-01-01 | Square Butte Coal-fired Unit | Minnesota Power      
Power Purchase Agreements [Line Items]      
Ppa counterparty annual debt service through 2027 $ 11.9